A subgroup is some slice of a process array, formed by restricting the process coordinates in one or more dimensions to single values.
Suppose i is a location in a range distributed over a dimension of group p. The expression
p / irepresents a smaller group--the slice of p to which location i is mapped.
Similarly, a subrange is a section of a range, parameterized by a global index triplet. Logically, it represents a subset of the locations of the original range.
The syntax for a subrange expression is
x [ 1 : 49 ]The symbol ``:'' is a special separator. It is used to compose a triplet expression with optional int expressions to represent an integer subset. The default initial and final values are respectively zero and the extent of the range. The default stride size is 1.